Recent results have shown that a wide gap in knowledge exists about cell dynamics and patterns of cell migration and differentiation in the upper airway epithelium of normal animals at different ages. The major objectives of this research are (a) to elucidate cell renewal mechanisms (proliferation and differentiation) in the tracheal epithelium of normal hamster at different ages and (b) to define the mechanisms of ciliogenesis in the trachea of such animals. We will examine the cell cycle kinetics of basal and mucous cells (labeling and mitotic indices), durations of cell cycle times and cell cyle phases, cell turnover times and the pathway of cell differentiation. The role of preexisting centrioles and the mechanism of transport of centrioles from the supranuclear to apical cytoplasm prior to ciliogenesis will be examined. Most studies will be accomplished using hamsters at ages of: fetal (18-20 days of gestation), 1 week, 4-6 weeks and 18 months old. Autoradiographic techniques at the light and electron microscope levels will be used. In addition ultrastructural techniques will be applied to define differentiation pathways of tracheal epithelial cells. In addition to elucidation of the basic cell renewal mechanisms in the tracheal epithelium, the results of this research will serve as a baseline for information against which alterations caused by environmental and infectious agents could be compared.